Which step in external respiration allows O2 to move from the external environment to the alveolar spaces

b. regulated is the actual answer to your question.

explanation:

i think that you are smart and you should fit for it out

well for one plants are always the producer, so a is the answer. a wolf is more of the consumer(predator) and the deer is the prey so i know those two are out of the question. also mushrooms are fungi/fungus so a is the producer.